The Problem: Particulates within air pollution are associated with significant morbidity and mortality at commonly encountered ambient concentrations. The biologic basis for their health effects is unknown, but the same epidemiologic studies which reveal particle effects also offer an important clue. Harmful health effects occur most notably among individuals with pre-existing respiratory disease, e.g. chronic bronchitis and asthma, indicating a heightened sensitivity to particle effects within inflammed lungs. Experimentally, we have found that inhalation exposure of animals to "real-world" concentrated ambient particulates (CAPs) prepared via a novel technology causes toxic effects--but only in animals with pre-existing pulmonary inflammation (asthma, SO2, bronchitis), and not in healthy controls. Hypothesis: The central thesis of this proposal is that pre-existing pulmonary disease alters or "primes" the lung's response to inhaled ambient particles, resulting in increased inflammation and health effects. We further postulate that oxidative stress mediated by particulate components is a central mechanism for increased production of inflammatory mediators by "primed" lung cells. Experimental Plan: In specific Aim #1 we will measure in vitro the production of reactive oxygen species, nitric oxide and cyrokines in response to uptake of CAPs by lung marcophages or epithelial cells with or without "priming" by inflammatory mediators (LPS, TNF). We will test our hypothesis regarding oxidant mechanisms of CAPs effects by: 1) measuring oxidant stress in primed and normal lung cells after uptake of CAPs (oxidation of intracellular reporter DCFH; lipid peroxidation); 2) analyzing oxidant components (e.g. SiO2, Fe) in samples of CAPs that vary in inflammatory effects; 3) testing the ability of antioxidants to block cellular responses. In specific Aim #2 we will characterize in vivo the effects of inhaled concentrated ambient particulates (CAPs) on pre-existing inflammatory lung disease using a mouse asthma model. We will test our hypotheses by inhalation exposure of normal and "asthmatic" mice to CAPs, measuring both lung lavage markers of cellular inflammation (total cells, number of eosinophils, cytokine levels) and physiologic tests of airway bronchoconstriction. To complete our study of mechanisms in vivo, we will also measure the effects of antioxidant intervention, both pharmacologic and through use of genetically altered mice. Significance: The proposed studies will determine mechanisms for the effect of air pollution particulates. Such informaiton is critical to public health management of this problem.